Generally, in the demolition of reinforced concrete buildings, a reinforcement shear mounted at the free end of the arm of a power shovel is employed. As an example of such shear, there is known a shear comprising a stationary lower jaw having a cutting edge and a movable upper jaw having an associated cutting edge and adapted to open and close with respect to said stationary lower jaw, said cutting edges being respectively straight edges (cf. Japanese Utility Model Application Kokai S-54-167871).
This type of shear having straight cutting edges as mentioned above can shear iron sheet and the like neatly but cannot shear reinforcing steel or the like because such a shearing load tends to slip forward unless fixed somehow in position.
To solve this problem, U.S. Pat. No. 4,519,135 proposes a shear illustrated in FIG. 6. This shear comprises a lower jaw I rigidly mounted on the arm 2 of a power shovel and an upper jaw 4 connected to said lower jaw 1 through a pivot 4 so that the upper jaw may open and close with respect to the lower jaw. In use of the shear, the steel reinforcement, for instance, is trapped between said upper and lower jaws and the upper jaw 4 is then closed by means of an associated hydraulic cylinder 5 to shear the reinforcement. In this shear, the upper and lower jaws are recessed away from each other in a longitudinally intermediate position to prevent forward displacement of the gripped load on shearing.
In addition, the upper jaw 4 is formed as a single member and the lower jaw 1 as two parallel members so that the forward end of the upper jaw 4 may descend into the clearance between the two members of the lower jaw 1. These two parallel members of the lower jaw 1 are interconnected by a front end member 6. The mating edge portions of the upper and lower jaws 1,4 are respectively provided with plural cutting edges 7,8,9,10. Moreover, wear plates 11,12 are rigidly secured to the upper and lower jaws, respectively, on the side opposite to said cutting edges 7,8,9,10 so that the upper jaw 4 will not be deflected sideways in shearing.
However, the proposed shear has the problem that the cutting edge 7 of the upper jaw 4 and that 9 of the lower jaw 1 are parallel even in the maximum opening position of the jaws and do not open further so that the maximum degree of opening cannot be large. In other words, generally any shear designed to preclude a forward slip of the gripped load cannot have a large opening.